Light emitting device

ABSTRACT

A light emitting device, free from change of color even when the wavelength of a light emitting element shifts, includes a light emitting element ( 106 ) for emitting primary light having an intensity peak at a wavelength shorter than 400 nm; a silicone resin ( 111 ) provided to embed the light emitting element; and a fluorescent element ( 110 ) contained in the silicone resin to absorb the primary light and release visible light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 10/118,612 filed Apr. 8,2002, the entire contents of which are incorporated by reference. Thisapplication is also based upon and claims the benefit of priority under35 U.S.C. § 119 from the prior Japanese Patent Application No.2001-110673, filed on Apr. 9, 2001; the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to a light emitting device, in particular,combining a light emitting element like a semiconductor light emittingelement and a wavelength converting means like a fluorescent element.

Light emitting devices combining LEDs (light emitting diodes) or othersemiconductor light emitting elements and fluorescent elements have beenremarked as inexpensive, long-lived light emitting devices, and theirdevelopment is being progressed. Light emitting devices of this typehave the advantage of providing emission colors conventionalsemiconductor light emitting elements could not realize.

Usually, semiconductor light emitting elements emit light uponre-combination of carriers injected into their active layers, andemission wavelengths are determined by energy band gaps of the activelayers. For example, monochromatic emission has been realized, such asred and yellow with semiconductor light emitting elements using InGaAlPcompounds, and green and blue with those using InGaN compounds.

However, to realize a certain mixed color by using those conventionalsemiconductor light emitting elements, it has been necessary to combinesome light emitting elements for different colors and control opticaloutputs of individual light emitting elements by adjusting their currentvalues. Therefore, the device configuration was inevitably complicatedand needed troublesome adjustment.

In contrast, light emitting devices configured to emit light bywavelength-converting light emitted from semiconductor light emittingelements by means of fluorescent elements are advantageous in realizinga color heretofore impossible with a single semiconductor light emittingelement by changing fluorescent elements or their combination.

A white light emitting device, described in “Compound Semiconductor”Vol. 5, No. 4, 00.28-31, is one of light emitting devices combiningsemiconductor light emitting elements and fluorescent elements. Thislight emitting device realizes white emission by mixture of two colorsfrom a semiconductor light emitting element for blue light and a YAG:Cefluorescent element excited by that blue light to emit yellow light.

FIG. 16 is a cross-sectional view illustrating a rough configuration ofa conventional light emitting device of this type. A semiconductor lightemitting element 802 is placed in an opening 801 formed in a package(resin stem) 800, and a sealing resin 804 is buried to encapsulate thesemiconductor light emitting element 802. The resin 804 contains afluorescent element 810.

The resin stem 800 has leads 805, 806 shaped from a lead frame, and aresin portion 803 molded to bury them. The semiconductor light emittingelement 802 is mounted on the lead 806, and connected to the lead 805 bya wire 808. The semiconductor light emitting element 802 is electricallyfed through two leads 805, 806 to emit light, and the fluorescentelement 810 absorbs the emitted light to release converted light. Thesemiconductor light emitting element 802 is a semiconductor that emitsblue light, and the fluorescent material 810 is YAG:Ce fluorescentelement that absorbs blue light from the light emitting element 802 andrelease yellow light.

With the light emitting device shown in FIG. 16, white light by mixtureof two colors, namely the blue light from the semiconductor lightemitting element 802 and the yellow light resulting from partialwavelength conversion by the fluorescent element 810, is extracted froma light release surface 812.

Through reviews, however, the Inventors have found that light emittingdevices as shown in FIG. 16 involve the below-listed problems.

(1) The white balance largely fluctuates among light emitting devices.

(2) The white balance largely changes with the current value supplied.

(3) The white balance largely changes with the ambient temperature.

(4) The white balance largely changes with life of the semiconductorlight emitting element 802.

All of those problems derive from essential characteristics of the bluelight emitting element 802 used as the semiconductor light emittingelement. That is, indium gallium nitride used as the light emittinglayer of the blue light emitting element 802 is difficult to controlstrictly, and subject to fluctuation of emission wavelength among waferson which it grows. In addition, it inherently varies largely in emissionwavelength with the current supplied to the light emitting element 802or with temperature. Furthermore, it exhibits a tendency of fluctuationof the emission wavelength while the supply of current and the emittingoperation are continued.

Once the wavelength of blue light released from the blue light emittingelement 802 fluctuates due to those reasons, its intensity gets out ofbalance with that of the yellow light from the fluorescent element 810,and their chromaticity coordinates will get out of order. It results inlarge changes of the white balance of the white light as the output ofthe device, and invites those problems, namely, fluctuation inbrightness (luminance) and color (tone) of the white light obtained, badreproducibility among products, and low mass productivity.

Moreover, the light emitting device shown in FIG. 16 inherently involvesanother problem that it is difficult to adjust the quantity of thefluorescent element in the resin enclosing the semiconductor element inaccordance with the luminance of the light emitting element. Especially,emission from YAG:Ce with a high visible sensitivity is difficult tocontrol because an error in quantity of the fluorescent element in theorder of several micro grams (μg) influences the tone and the luminance.

Furthermore, this light emitting device is operative only in a narrow,limitative temperature range. If it is operated under, for example, 50°C. or higher temperature, the tone changes to bluish white. Such atemperature-caused change of color occurs due to a difference intemperature characteristics between the semiconductor element and thefluorescent element, namely because degradation of emission efficiencyof the fluorescent element under a high temperature is larger than thatof the degradation of emission efficiency of the semiconductor.

In addition, in case of the light emitting device shown in FIG. 16, theresin 804 containing the fluorescent element 810 for yellow emission hasa “yellow” tone in its OFF state. That is, since the part lit “white” inthe ON state looks “yellow” in the OFF state, its “appearance” is notgood.

SUMMARY OF THE INVENTION

According to an embodiment of the invention, there is provided a lightemitting device comprising: a light emitting element which emits primarylight; a silicone resin provide to embed said light emitting element andhaving a hardness in the range of 50 to 90 in JISA value; and afluorescent element contained in said silicone resin to absorb saidprimary light and release visible light.

The present application contemplates, with the term “silicone resin”,any resin having as its skeleton a structure in which silicon atomshaving organic radicals such as alkyl radicals or aryl radicals arealternately connected to oxygen atoms. Needless to say, those containingadditive elements added to such skeletons are also included in “siliconeresins”.

In the present application, the “fluorescent element” may be any havinga wavelength converting function, either inorganic and organic,including inorganic dyes having a wavelength converting function.

In the present application, “nitride semiconductors” include III-Vcompound semiconductors expressed by the chemical formulaB_(x)In_(y)Al_(z)Ga_((1−x−y−z))N (0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦x+y+z≦1) whereeach of x, y, and z is varied throughout its respective range, andfurther include mixed crystals containing not only N (nitrogen) but alsophosphorus (P) and/or arsenic (As) in addition to N as group V elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given here below and from the accompanying drawings of theembodiments of the invention. However, the drawings are not intended toimply limitation of the invention to a specific embodiment, but are forexplanation and understanding only.

In the drawings:

FIG. 1 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the first embodiment of the invention;

FIG. 2 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting device usablein the present invention;

FIG. 3 is a cross-sectional view that shows a light emitting device asthe second specific example usable in the present invention;

FIG. 4 is a cross-sectional view that shows a light emitting device asthe third specific example usable in the present invention;

FIGS. 5A through 5C show schematic diagrams that illustrate intensityprofiles of emitted light depending upon the surface configuration of asealing element;

FIG. 6 is a graph that shows measured changes of chromaticity x withcurrent-supply time;

FIG. 7 is a diagram that schematically illustrates a planarconfiguration inside an opening of a light emitting device according tothe embodiment of the invention;

FIG. 8 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the second embodiment of the invention;

FIG. 9 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the third embodiment of the invention;

FIG. 10 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the fourth embodiment of the invention;

FIG. 11 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the fifth embodiment of the invention;

FIG. 12 is a cross-sectional view that shows a modification of the fifthembodiment of the invention;

FIG. 13 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the sixth embodiment of the invention;

FIG. 14 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the seventh embodiment of the invention;

FIG. 15 is a cross-sectional view that shows a modification of theseventh embodiment of the invention; and

FIG. 16 is a cross-sectional view that shows an outline configuration ofa conventional light emitting device.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a light emitting device configured to emit lightresulting from wavelength conversion of primary light of a shorterwavelength from a semiconductor light emitting element by means of afluorescent element, and excellent in wavelength stability andreproducibility of the emission characteristics.

Some embodiments of the invention will now be explained below withreference to the drawings.

FIRST EMBODIMENT

FIG. 1 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the first embodiment of the invention.

The light emitting device 1A shown here includes a resin stem 100, asemiconductor light emitting element 106 mounted on the resin stem 100,and a sealing element 111 provided to embed the element 106.

The resin stem 100 includes leads 101, 102 shaped from a lead frame, anda resin portion 103 molded integrally with the leads 101, 102. The leads101, 102 have opposed ends close to each other, and extend therefrom inthe opposite directions to outside the resin portion 103.

The resin portion 103 has an opening 105, and the semiconductor lightemitting element 106 is mounted on the bottom of the opening 105. Theplanar geometry of the opening 105 may be elliptical or circular, forexample. The inner wall surface of the resin portion 103 surrounding theelement 106 inclines toward the light releasing direction to serve as areflection surface 104 for reflecting light.

The light emitting element 106 is mounted on the lead 101 on the bottomsurface of the opening 105 with an adhesive such as silver (Ag) paste.The light emitting element 106 has first and second electrodes (notshown) that are connected to the leads 101, 102 by bonding wires 108,109 of gold (Au) for example.

The sealing element 111 buried in the opening 105 contains a fluorescentelement 110. In the embodiment shown here, the light emitting element106 may have the emission peak at a wavelength shorter than 400 nm, andthe fluorescent element 110 may be a substance excited by primary lightof a wavelength shorter than 400 nm. The fluorescent element 110 may beeither a single substance or a combination of, for example, afluorescent element 110A releasing red light, fluorescent element 110Breleasing green light, and fluorescent element 110C releasing bluelight. Other various combinations are also acceptable as explainedlater.

The basic concept of the invention is to extract light converted inwavelength from primary light by the fluorescent element 110 instead ofdirectly extracting the primary light emitted from the light emittingelement 106. That is, ultraviolet or other light emitted from the lightemitting element 106 is converted in wavelength by the fluorescentelement 110 (for example, red fluorescent element 110A, greenfluorescent element 110B and blue fluorescent element 110C), andextracted as a mixed color of such secondary light.

This way of extraction can overcome the problem of the change of colorcaused by differences or variances of emission characteristics betweenthe light emitting element 106 and the fluorescent element 110. Forexample, even if the wavelength of the light emitting element 106 amongproducts, or the wavelength of the light emitting element 106 shiftsfrom the original value due to temperature conditions, changes withtime, or the like, influences thereof to the fluorescent element aresmall, and the balance of the mixed color obtained from the fluorescentelement does not almost change. Therefore, the invention can realize alight emitting device remarkably stable in emission characteristics overa wide temperature range and a wide range of operation time.

In addition, when the fluorescent element used in the invention is of amixed type combining, for example, the red fluorescent element 110A,green fluorescent element 110B and blue fluorescent element 110C, and iscontained in a transparent resin, the sealing element 111 exhibits a“white” tone. That is, it looks “white” in the OFF state, and emitswhite light in the ON state. Therefore, it has a good appearance, andthis feature is significantly advantageous from the visual viewpointwhen it is used in various applications.

The material used as the sealing element 111 is also an importantfeature of the invention. The use of a silicone resin instead ofconventional epoxy resin contributes to ensuring a sufficient durabilityeven against light of short wavelengths whose peak wavelengths areshorter than 400 nm.

The sealing element 111 is preferably of a type having a high viscositybefore its sets. The sealing element 111 of this type makes it difficultfor the fluorescent element 110 to move and locally concentrate, andthereby prevents its sedimentation or segregation even when the sealingelement 111 mixed and shaken with the fluorescent element 110 is leftfor a long time. Especially when different kinds of fluorescent elementsare mixed, sedimentation or segregation of the fluorescent elements willinvite chromatic irregularity and variances of luminance. However, byadjusting the prior-to-curing viscosity, it is possible to keep thefluorescent element 110 uniformly dispersed in the sealing element 111without being localized and thereby stabilize the emissioncharacteristics.

In a practical case using a light emitting element 106 having a size inthe range of 50 μm to 1000 μm, each side, and a thickness in the rangeof 10 μm through 1000 μm, adjusting the mixture ratio of fluorescentelement 110 in the range from 1 weight % to 50 weight %, and selectingthe viscosity of the resin upon curing in the range from 100 cp(centipoise) through 10000 cp, even when the fluorescent element 110 wasa mixture of some kinds of fluorescent materials different in gravityand grain size, the fluorescent material was uniformly dispersed in thesealing element 111 without segregation or like undesirable phenomenon,and uniform emission was attained. That is, light emitting elementseliminating chromatic irregularity and having a high luminance could berealized.

As roughly explained above, according to the embodiment of theinvention, since the light emitting element 106 is located on the bottomsurface of the packaging member 100 like the resin stem, and thefluorescent element 110 is dispersed in the sealing element 111 havingthe unique features, such that all particles of the fluorescent elementcan emit light even under segregation of the fluorescent particles dueto differences in specific gravity and grain size, high-yield productionis ensured minimizing tone variances and degradation of luminance.

Next explained are greater details of individual components of the lightemitting device according to the embodiment of the invention.

(Re: Light Emitting Elements 106)

The light emitting element 106 has a multi-layered structure including alight emitting layer of a nitride semiconductor formed on apredetermined substrate by a crystal growth method such as metal-organicchemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

The light emitting element preferably has a “double heterostructure” inwhich the light emitting layer of a nitride semiconductor is sandwichedfrom the top and the bottom by layers having a larger band gap. Thedouble heterostructure ensures stable characteristics that hold changesof the emission wavelength with time within 50 nm in the range oftemperature changes from −40° C. to 100° C., and its changes withcurrent within 50 nm in the range of current changes from 1 mA to 100mA.

FIG. 2 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting device usablein the present invention. The light emitting element 106 A includes abuffer layer 122 of AlN, n-type GaN contact layer 123, light emittinglayer 124, p-type GaAlN cladding layer 125, and p-type GaN contact layer126 that are sequentially formed on a sapphire substrate 121. The lightemitting layer 124 has a quantum well (QW) structure in which GaNbarrier layers and InGaAlN well layers are stacked alternately.

On the n-type GaN contact layer 123 exposed by selectively removing themulti-layered structure by etching from its surface, an n-side electrode127 made of Ti/Al is formed. On the other hand, formed on the p-type GaNcontact layer 126 are a translucent p-side electrode 128 in form of aNi/Au thin film having a thickness of tens of nanometers and a bondingpad 129 of gold (Au) connected to the p-side electrode 128. Surface ofthe element is covered by a protective film 130 of SiO₂.

When a voltage is applied to the n-side electrode 127 and the p-sideelectrode 128 of the light emitting element 106A, light generated in thelight emitting layer 124 is released from the surface 131. Since theintensity of the emission peak wavelength can be enhanced by providing aplurality of ripples in the emission spectrum, absorption. of theexcited fluorescent element is enhanced, and a light emitting devicewith a high luminance can be realized.

The emission wavelength is determined variously by changing thecomposition of the semiconductor materials of the light emitting layer124 (for example, composition of well layers of QW), ultraviolet lightwhose wavelength is in the range from 200 nm to 400 nm can be obtained.Ultraviolet light of a wavelength in the range from 250 nm to 400 nm isdesirable because a large quantity is absorbed by the fluorescentelement. Ultraviolet light having a wavelength in the range from 370 nmto 400 nm is more desirable because it increases the emission efficiencyof the light emitting element 106. Ultraviolet light having a wavelengthin the range from 380 nm to 400 nm is still more desirable because itprevents deterioration of the sealing element 111 embedding the lightemitting element 106.

The light emitting element 124 preferably has a single quantum wellstructure including a single layer having a quantum effect and athickness in the range from 1 nm to 20 nm, or a multiquantum wellstructure two or more such layers because it narrows the spectral widthand increases the excitation efficiency of the fluorescent element 110.The light emitting layer 124 is preferably in form of dots each sizedseveral nanometers to several micrometers in its plan-viewedconfiguration, thereby to improve the emission efficiency and theexcitation efficiency of the fluorescent element.

Impurities such as silicon (Si), zinc (Zn) or germanium (Ge) arepreferably added to the light emitting layer 124 to decrease thepiezoelectric field generated by distortion caused by latticemiss-matching and to promote recombination of injected carriers andincrease the emission efficiency of the light emitting element.

On the other hand, regarding the substrate 121, n-type GaN, n-type ZnO,insulating quartz, or the like, are usable materials in addition tosapphire. Sapphire has a high transmittance to wavelengths shorter than400 nm, and permits light from the light emitting layer 124 to beeffectively extracted without absorbing it.

If a conductive substrate of n-type GaN, for example, is used, itenables to decrease the gold (Au) wire exhibiting a low reflectanceagainst light of wavelengths shorter than 400 nm to only one, and canthereby improve the extraction efficiency of emitted light. Furthermore,the light extraction efficiency can be improved by reflecting the lightfrom the light emitting layer 124 with the electrode at the back surfaceof the conductive substrate. Here is also the additional advantage thatdeterioration of the adhesive 107 used to mount the light emittingelement 106 by light is alleviated, and it also increases thereliability of the light emitting device.

In case a sapphire substrate is used, by first forming the buffer layer122 and the n-type GaN layer 123 are formed on the substrate 121 andthereafter forming a second buffer layer of AlN under a lower growthtemperature, it is possible to improve the crystallographic property ofthe light emitting layer 124, thereby decrease the crystallographicdefects in the light emitting layer and improve the emission efficiencyof the light emitting element. it simultaneously contributes to adecrease of absorption of secondary light from the fluorescent element110 by crystallographic defects, improvement of the reliability, andenhancement of the luminance of the light emitting device.

Material of the buffer layer 122 is not limited to AlN, but GaN, AlGaN,InGaN and InGaAlN are also acceptable either individually as a singlelayer or in combination as a multi-layered film. The buffer layer 122preferably has a thickness in the range from several nanometers tohundreds of nanometers to prevent absorption of light from thefluorescent element not to degrade the luminance.

Material of the n-type layer 123 is not limited to GaN, but AlGaN, InGaNand InGaAl are also acceptable either individually as a single layer orin combination as a multi-layered film. Its thickness is preferablyadjusted in the range from 1 μm to 10 μm to ensure uniform flow of theinjected current inside the n-type layer 123, uniform emission of thelight emitting element and efficient excitation of the dispersedparticles of the fluorescent element. The impurity added to the n-typelayer 123 is preferably silicon (Si), germanium (Ge) or selenium (Se) toreplace point defects of the semiconductor crystal, thereby preventmigration of the fluorescent element into the semiconductor duringapplication of a current, and hence improve the reliability.

Material of the p-type layer 125 is not limited to AlGaN, but InAlGaNand InGaN are also acceptable either individually as a single layer orin combination as a multi-layered film. Its thickness is preferablyadjusted in the range from several nanometers to several micrometers toalleviate that the carriers once injected into the light emitting layer124 overflows therefrom, thereby to improve the emission efficiency ofthe light emitting element 124. The impurity added to the p-type layer125 is preferably magnesium (Mg) or zinc (Zn) to prevent migration ofthe fluorescent element into the semiconductor by replacing the pointdefects in the semiconductor crystal during the supply of a currentunder a high temperature.

Material of the p-type contact layer 126 is not limited To GaN, butAlGaN, InGaN and InGaAlN are also acceptable either individually as asingle layer or in combination as a multi-layered film. When asuperlattice structure of a. plurality of thin films of a thicknessaround several nanometers is used as such a multi-layered film, itcontributes to increasing the activated ratio of the p-type impurity,lowering the Schottky barrier with respect to the transparent electrode128 and decreasing the contact resistance. It results in minimizinginfluences of heat generation to the fluorescent element around thelight emitting element and maintaining a high luminance up to hightemperature ranges.

Material of the n-side electrode is not limited to Ti/Al, but scandium(Sc), yttrium (Y), lanthanum (La), zirconium (Zr), hafnium (Hf),vanadium (V) , niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum(Mo), aluminum (Al) or gold (Au) are also acceptable either individuallyor in combination as a multi-layered form or as an alloy.

Material of the p-side electrode 128 is not limited to Ni/Au, butpalladium (Pd), platinum (Pt), cobalt (Co), rhodium (Rh), iridium (Ir),nickel oxide (NiO), copper (Cu), aluminum (Al), magnesium (Mg),magnesium oxide (MgO) or silver (Ag) either individually or incombination as a multi-layered form or alloy.

The protective film 130 functions both to protect the thin-filmtransparent electrode 128 and to prevent migration of the fluorescentelement 110 into the transparent electrode 128 during the electricalsupply. Its material is not limited to SiO₂, but dielectric materialssuch as siliconnitride (SiN_(x)) or aluminum oxide (Al₂O₃) are alsousable.

FIG. 3 is a cross-sectional view that shows a light emitting device asthe second specific example usable in the present invention. The lightemitting element 106B shown here includes a reflective film 141 formedon the back surface of the sapphire substrate 121 added to the lightemitting element 106A of FIG. 2. A material having a high opticalreflectance, such as aluminum (Al), may be used as the material of thereflective film 141.

A metal film as the reflective film 141 formed on the back surface ofthe sapphire substrate 121 functions to reflect the light from the lightemitting element 124 toward the emission surface 131 and efficientlyextract the light generated in the light emitting element outside theelement. It also contributes to preventing the change of quality ordeterioration of the adhesive 107 due to primary light of a shortwavelength from the light emitting layer 124, change of color of thelead 101, change of color of the resin stem 100, and so on. The effectof preventing degradation of the adhesive strength of the adhesive 107is large. Furthermore, since the metal film 141 has a high thermalconductivity and improves the heat discharge effect, it can dischargethe heat generated in the light emitting layer 124 during operationunder a high current or a high temperature to the exterior of the lightemitting element, and can thereby minimize degradation of the luminanceby heat generation.

Usable materials as the material of the reflective film 141 are nickel(Ni), silver (Ag), chromium (Cr), titanium (Ti), copper (Cu) and gold(Au), in addition to aluminum, either individually or in combination asa multi-layered form or an alloy.

FIG. 4 is a cross-sectional view that shows a light emitting device asthe third specific example usable in the present invention. The lightemitting element 106C shown here is a modification of the light emittingelement 106A of FIG. 2, in which the transparent p-side electrode 128 isreplaced by a p-side electrode 161 in form of a metal layer thatreflects light from the light emitting layer 124. The metal layerforming the p-side electrode 161 may have a thickness larger thanhundreds of nanometers.

Light from the light emitting layer 124 is reflected by the p-sideelectrode 161, and can be extracted from the emission surface 171without being absorbed by the sapphire substrate 121. The light emittingelement 106C shown here can increase the optical output to 1.5 two 2times as compared with the light emitting element 106A or 106B, andtherefore, a light emitting device using this light emitting element106C and including a fluorescent element can realize a luminance as highas 1.5 to 2 times.

The p-side electrode 161 also contributes to preventing entry of thelight from the light emitting layer 124 into the adhesive 107 thereby toprevent deterioration of the adhesive 107 and also to preventdeterioration and change of color of the lead 101 and the resin stem 100around the light emitting element by light.

Furthermore, heat generation by voltage drop in the p-type layers 125,126, as a part of sources of heat generation of the light emittingelement, can be released to the lead 101 through the p-side electrode161.

Simultaneously, the light emitting element 106C can minimize influencesof heat generation in the light emitting element and can thereby preventdeterioration of the fluorescent element by high temperatures by keepingthe heat generation sources like the p-type layers and light emittinglayer 124 away from the fluorescent element 110. As a result, the lightemitting device is operative under high temperatures, and itsreliability is improved.

The use of the light emitting element 106C also makes it possible todirectly connect two leads 101, 102 without using a gold (Au) wire. Itresults in eliminating the problem of breakage of the gold (Au) wire dueto a stress to the resin, thereby improving the reliability, andsimultaneously realizing a high luminance by eliminating absorption oflight from the light emitting element by the gold wire.

Furthermore, the crystal growth layers 122 through 126 grown on thesapphire substrate 121 can be separated from the fluorescent element111, and therefore, the device can operate without influences of raisedtemperatures of the fluorescent element caused by non-emission by thefluorescent element, and the reliability of the device increases.

The material of the p-side electrode 161 is preferably selected fromnickel (Ni), cobalt (Co), antimony (Sb), magnesium (Mg), silver (Ag),platinum (Pt) and palladium (Pd) that are materials having smallSchottky barriers with respect to the p-type GaN layer 126.Alternatively, aluminum (Al) or silver (Ag), which is a high-reflectancematerial to reflect light from the light emitting layer 124, ispreferably used. Alternatively, molybdenum (Mo), platinum (Pt),palladium (Pd), nickel (Ni) or gold (Au), which is less reactive to theadhesive 107, is preferably used.

In case those materials are used in form of a multi-layered structure, ametal film having a small Schottky barrier is preferably formed as athin film having a thickness in the range from several nanometers ortens of nanometers to minimize absorption of light such that thequantity of light entering into the underlying high-reflectance metallayer increases.

(Re: Adhesive 107)

In order to mount the light emitting element 106, a paste containingsilver (Ag), for example, is used as the adhesive 107. However, Othermaterials are also acceptable.

Ag paste has a high adhesive force with respect to the light emittingelement 106 and the lead 101, and can maintain the mounting strengtheven upon sudden changes of the temperature. Additionally, Ag containedin the paste enables effective heat discharge therethrough and canprevent the light emitting layer 124 from a rise of the temperature.Furthermore, Ag can reflect primary light from the light emittingelement 106, and can therefore reflect light emitted toward the sapphiresubstrate 121 back to the emission surface 112.

Ag paste is preferably provided to project from the side surface of thesapphire substrate 121 not only to increase the adhesive strength butalso to reflect light going out of the side surface of the sapphiresubstrate 121 back to the emission surface of the light emitting element131, thereby to realize a high luminance.

Various materials other than Ag paste are also usable as the adhesive107. Such. examples are silicone-based adhesives including no metal,epoxy-based adhesives that are transparent to light of wavelengthsshorter than 400 nm, eutectic alloy solders such as gold-tin (AuSn),gold-germanium (AuGe), etc.

Silicone-based adhesives are reliable because of less change of color byemission of light and less deterioration of the adhesive force.

Epoxy-based adhesives are more likely to change in color by emission oflight, and metals and/or scattering agents for reflecting light arepreferably added to prevent changes of color. When they are combinedwith light emitting elements 106B, 106C having reflective films onsurfaces opposed to adhesives, reliable light emitting devices can berealized. Additionally, epoxy-based adhesives are advantageous for massproduction because of their close fitting to leads for mounting elementson, decrease of exfoliation of the light emitting elements, and highcontrollability of the quantity of paste.

The bonding method using a metal eutectic alloy solder is highlyeffective for light emitting elements such as light emitting elements106B, 106C using conductive substrates like the n-type GaN substrate.Metal eutectic exhibits a high bonding force, eliminates color change orother deterioration caused by light from the light emitting layer 124,and excellent heat dissipation. However, because of its high bondingforce, light emitting elements may receive influences of a heat stressduring operation under high temperatures. This stress, however, can bereduced by forming a metal film containing gold (Au) and having athickness of several micrometers on the bonding surface of the lightemitting element.

(Re: Resin Portion 103)

The resin portion 103 has an opening 105. The light emitting element106, end portions of the first and second leads 101, 102, Zener diode(not shown), etc. are located in the opening 105.

The opening 105 has a narrower bottom and a wide open top to defineslanted a side wall as a reflective surface 104 that reflects primarylight from the light emitting element 106 and light from the fluorescentelement 110.

The resin portion 103 has a property of reflecting light primary lightfrom the light emitting element 106 and light converted by thefluorescent element 110. It is made of, for example, 65 or more weight %of a thermoplastic resin and 35 or less weight % of a filling agent. Thefilling agent contains a high-reflective material such as titanium oxide(TiO₃), silicon oxide, aluminum oxide, silica or alumina. In case oftitanium oxide, its content is in the range from 10 to 15%. Because thereflective surface 104 is a part of the resin portion containing adiffusing material that reflects light, it can reflect light from thelight emitting element 106 and the fluorescent element 110 upward torealize a high luminance of the light emitting device. If the reflectivesurface 104 is configured as a paraboloid of revolution, for example,the output and the quality of the light emitting device can be furtherimproved.

The thermoplastic resin may be a resin having a high resistance to heat,such as liquid crystal polymer (LCP), polyphenylene sulfide (PPS:thermoplastic resin) or syndiotactic polystyrene (SPS: crystallinepolystyrene). The plan-viewed outer configuration of the resin portion103 may be a substantial square approximately sized 2.0×2.0 mm through6.0×6.0 mm, or a substantial rectangular approximately sized 2.0×3.0 mmthrough 5.0×7.0 mm. The light emitting element 106 is located offsetfrom the center on the bottom surface of the cavity 105. This offsetplacement of the light emitting element is for the purpose of making anample region for the bonding wire and locating a side surface of thelight emitting element 106 closed to the reflective surface 104 toincrease the reflectance and realize a high luminance.

The top and bottom of the opening 105 of the resin portion 103 may beelliptical (with a longer diameter of 1 to 2.8 mm and a shorter diameterof 0.5 to 2.7 mm). Since the bottom is narrow, when the sealing element110 containing uniformly dispersed particles of the fluorescent element110 is buried in the opening 105, the quantity of the fluorescentelement 110 is less near the light emitting element 106 and more andmore toward the top. Therefore, primary light emitted from the lightemitting element 106 is absorbed and converted to second light by thefluorescent element 110 by a progressively large quantity as it goesapart from the light emitting element, and finally, substantially all ofprimary light can be converted to secondary light. At the same time, itis possible to reduce the probability that the converted secondary lightis absorbed by other fluorescent elements.

(Re: Fluorescent Element 110)

The fluorescent element 110 used in the embodiment of the invention is afluorescent material that releases light by absorbing ultraviolet lightshorter than 400 nm emitted from the light emitting layer 124 of thelight emitting element 106, or a material that releases light byabsorbing light emitted from another fluorescent element. Thefluorescent element 110 preferably has a conversion efficiency of 1lumen/watt or more.

White light can be realized by mixing three primary colors of red, greenand blue, or by mixing any two complementary colors. White light bythree primary colors can be realized by using a first fluorescentelement for releasing blue light by absorbing light from the lightemitting element 106, a second fluorescent element for releasing redlight, and a third fluorescent element for releasing green light.

White light by complementary colors can be realized by combining a firstfluorescent element for releasing blue light by absorbing light from thelight emitting element 106 and a second fluorescent element for emittingyellow light by absorbing the blue light, or by combining a firstfluorescent element for releasing green light by absorbing light fromthe light emitting element 106 and a second fluorescent element forreleasing red light by absorbing the green light.

Fluorescent elements whose wavelength changes are not larger than 50 nmin the temperature range from −40 ° C. to 100 ° C. are preferably usedto realize a light emitting device independent from temperaturecharacteristics of the light emitting element.

The use of fluorescent elements whose wavelength changes do not exceed50 nm when the light emitting element 106 is operated by a drive currentin the range from 1 mA to 100 mA enables realization of a light emittingdevice independent from changes in emission spectrum caused by the drivecurrent of the element.

There are the following fluorescent materials that can release bluelight.

ZnS:Ag

ZnS:Ag+Pigment

ZnS:Ag, Al

ZnS:Ag, Cu, Ga, Cl

ZnS:Ag+In₂O₃

ZnS:Zn+In₂O₃

(Ba, Eu)MgAl₁₀O₁₇

(Sr, Ca, Ba, Mg)₁₀(PO₄)₆Cl₂:Eu

Sr₁₀(P0 ₄)₆Cl₂:Eu

(Ba, Sr, Eu) (Mg, Mn) Al₁₀O₁₇

10 (Sr, Ca, Ba, Eu)≅6PO₄≅Cl₂

BaMg₂Al₁₆O₂₅:Eu

There are the following fluorescent elements that can release greenlight.

ZnS:Cu, Al

ZnS:Cu, Al+Pigment

(Zn, Cd)S:Cu, Al

ZnS:Cu, Au, Al, +pigment

Y₃Al₅O₁₂:Tb

Y₃(Al, Ga)₅O₁₂:Tb

Y₂SiO₅:Tb

Zn₂SiO₄:Mn

(Zn, Cd)S:Cu

ZnS:Cu

Zn₂Si₄:Mn

ZnS:Cu+Zn₂SiO₄:Mn

Gd₂O₂S:Tb

(Zn, Cd)S:Ag

ZnS:Cu, Al

Y₂O₂S:Tb

ZnS:Cu, Al+In₂O₃

(Zn, Cd)S:Ag+ In₂O₃

(Zn, Mn)₂SiO₄

BaAl₁₂O₁₉:Mn

(Ba, Sr, Mg)O≅aAl₂O₃:Mn

LaPO₄:Ce, Tb

Zn₂SiO₄:Mn

ZnS:Cu

3 (Ba, Mg, Eu, Mn)O≅8Al₂O₃

La₂O₃≅0.2SiO₂≅0.9P₂O₅:Ce, Tb

CeMgAl₁₁O_(19:Tb)

There are the following fluorescent materials usable to release redlight.

Y₂O₂S:Eu

Y₂O₂S:Eu+pigment

Y₂O₃:Eu

Zn₃(PO₄)₂:Mn

(Zn, Cd) S:Ag+In₂O₃

(Y, Gd, Eu) BO₃

(Y, Gd, Eu)₂O₃

YVO₄:Eu

La₂O₂S:Eu, Sm

The following fluorescent material, for example, can be used forreleasing yellow light.

YAG:Ce

By using those red fluorescent elements, green fluorescent elements andblue fluorescent elements in an appropriate adjusted R:G:B ratio, anydesired tone can be made. For example, white colors from white lampcolor to white fluorescent lamp color can be realized by one of 1:1:1through 7:1:1, 1:1:1 through 1:3:1 and 1:1:1 through 1:1:3 in R:G:Bweight % ratio.

When the total weight percent of the mixed fluorescent elements isadjusted in the range from 1 weight % to 50 weight % relative to theweight of the sealing element containing the fluorescent elements,substantial wavelength conversion is realized. When it is adjusted inthe range of 10 weight % to 30 weight %, a light emitting device with ahigh luminance is realized.

In case those RGB fluorescent elements are appropriately selected andmixed, the tone of the sealing element 111 will become white. That is,since the light emitting device emitting white light looks white also inthe OFF state, its appearance is good, and a light emitting deviceexcellent from the visual and design viewpoints can be provided.

Fluorescent materials usable in the invention are not limited toinorganic fluorescent materials. High-luminance light emitting devicescan be realized also by similarly using the following organic dyematerials.

xanthene dyes

oxazine dyes

cyanine dyes

rhodamine B (630 nm)

coumarin 153 (535 nm)

polyparaphenylene vinylene (510 nm)

coumarin 1 (430 nm)

coumarin 120 (450 nm)

tris-(8-hydroxyquinoline) aluminum (Alq3 or AlQ) (green light)

4-dicyanomethylene-2-methyl-6(p-dimethylaminostyrene)-4H-pyran (DCM)(orange/red light)

Also when some kinds of dye materials are used, individual dye materialscan be dispersed in the resin by adding respective dye materials into asilicone resin as the sealing element and stirring it, and excitationefficiency of dyes can be enhanced.

According to the embodiment of the invention, various colors of lightcan be realized with the light emitting device by combining appropriatematerials of the fluorescent element (including dyes) 110 contained inthe sealing element 111. That is, any desired tone can be realized bycombining red, green, blue and yellow fluorescent materials (and dyes).

On the other hand, the embodiment of the invention can also realizestabilization of the emission wavelength, which could not attained withconventional semiconductor light emitting elements, even by using asingle fluorescent element. That is, ordinary semiconductor lightemitting elements are subject to shifting of the emission wavelengthdepending on the drive current, ambient temperature and modulatingconditions. In contrast, in the light emitting device according to theembodiment of the invention, the emission wavelength is remarkablystable, independently of changes of the drive current and temperature.

In addition, the emission characteristics of the light emitting deviceaccording to the embodiment of the invention is determined by thecharacteristics of the additive fluorescent element 110 regardless ofcharacteristics of the light emitting element 106, the production yieldcan be increased without variances of characteristics among differentlight emitting devices.

(Re: Surface Configuration of the Sealing Element 111)

The sealing element 111 is a member containing the fluorescent element110 buried in the opening 105 to convert primary light from the lightemitting element 106. For this purpose, the sealing element 111 ispreferably made of a material having a larger coupling energy than theenergy of the primary light from the light emitting element 106.Additionally, it preferably has the property of transmitting light afterwavelength conversion by the fluorescent element 110.

The Inventors have got new knowledge about the surface configuration ofthe sealing element 111 through his own trial and review about it.

FIGS. 5A through 5C show schematic diagrams that illustrate intensityprofiles of emitted light depending upon the surface configuration ofthe sealing element. The profile of FIG. 5A is the intensity profile Pof light from the light emitting element 106 using a sealing element 111having a flat surface configuration, the profile of FIG. 5B is that witha sealing element 111 having a concave surface configuration, and theprofile of FIG. 5C is that with a sealing element 111 having a convexsurface configuration.

In comparison with the case of the flat configuration shown in FIG. 5A,the intensity profile, i.e. orientation characteristics, of the emittedlight of the device having the concave surface configuration shown inFIG. 5B apparently converges in the direction of the vertical axis Z. Incontrast, the profile corresponding to the convex surface configurationshown in FIG. 5C diverges in the direction of the xy plane. Its reasonmight be that the light emitted from the fluorescent element containednear the convex portion of the sealing element 111 having the convexsurface configuration spreads in the xy plane direction whereas thelight emitted from the fluorescent element contained near the surface ofthe sealing element having the concave surface configuration isreflected by the side wall reflective surface 104 and contributes toincrease the ratio of light traveling in the z-axis direction.

The surface configuration of the sealing element 111, either convex orconcave, can be determined by adjusting its quantity to be buried. Thatis, by adjusting the filling quantity of the sealing element 111, anydesired orientation characteristics of the emitted light can beobtained.

In case a plurality of light emitting devices are arranged in parallelas a planar type image display apparatus, the convex surfaceconfiguration of the sealing element 111 may generate undesirableexcited light in receipt of the light from adjacent light emittingdevices. Therefore, the sealing element 111 preferably has a concavesurface configuration also in applications of this kind.

The embodiment of the invention can reliably, readily cope with thoserequirements by adjustment of the filling quantity of the sealingelement 111.

(Re: Material of the Sealing Element 111)

The sealing element 111 is a member containing the fluorescent element110 buried in the opening 105 to convert primary light from the lightemitting element 106. For this purpose, the sealing element 111 ispreferably made of a material having a larger coupling energy than theenergy of the primary light from the light emitting element 106.Additionally, it preferably has the property of transmitting light afterwavelength conversion by the fluorescent element 110.

If, however, the emission peak wavelength of the light emitting element106 is shorter than 400 nm, epoxy resins conventionally used as thematerial of the sealing element 111 are subject to rapid deterioration.More specifically, in receipt of primary light from the light emittingelement 106, epoxy resins, originally transparent, change in colorthrough yellow, liver to black, and it results in a serious decrease ofthe light extraction efficiency.

Through trials and reviews, the Inventors have found that the use ofsilicone resin leads to a very satisfactory result. That is, if asilicone resin is used, change or color and other types of deteriorationdo not occur even after it is exposed to short wavelength light havingthe peak wavelength below 400 nm. By actually using silicone resin in alight emitting device using short-wavelength light as primary light, ahigh reliability could be realized.

That is, silicone resins have the property of transmitting primary lightfrom the light emitting element 106 and light from the fluorescentelement 110 and ensuring a luminous intensity of the light emittingdevice not less than 60% of the initial luminous intensity even afteroperation of 1000 hours.

In a manufacturing process, silicone resin containing the fluorescentelement 110 is coated onto the light emitting element 106 mounted in theopening 105 by supplying it through a narrow nozzle while agitating itto uniformly mix predetermined fluorescent materials, and it isthereafter hardened.

In this process, it is preferable to use a silicone resin having apre-curing viscosity around 100 cp through 10000 cp because it can holdparticles of the fluorescent element uniformly dispersed withoutsegregation or segmentation. In this manner, light from the excitedfluorescent element is uniformly, adequately spread by a fluorescentelement having a large refractive index without being excessively spreador absorbed by other fluorescent elements. Therefore, light is uniformlymixed, and tone irregularity can be prevented.

The silicone resin used in the embodiment of the invention has a highbonding force to the resin portion 103 and a high strength to humidity,and it is unlikely to crack even under a temperature stress.Additionally, the silicone resin buried in the opening can greatlyalleviate the resin stress to the light emitting element 106 and the Auwire even upon changes of the ambient temperature.

The Inventors further developed researches from those viewpoints. As aresult, it has been found that the use of “rubber-like”, silicone resinhaving a high harness leads to an excellent result. Hardness of ordinarysilicone resins ranges from 30 to 40 in JISA harness value that is thehardness of the JIS standard. These silicone resins exhibit gel-likephysical properties, and are physically soft. Those silicone resins arehereinbelow called “gel-like silicone resins.

In contrast, “rubber-like silicone resins” have a JISA hardness in therange of approximately 50 to 90. Epoxy resins widely used as the sealingelement materials in conventional light emitting devices have a JISAhardness around 95.

The Inventors compared and reviewed both “rubber-like silicone resins”and “gel-like silicone resins”, and has got the following knowledge.

(1) When gel-like silicone was used, the fluorescent element 110 spreadin the resin during the supply of a current, and there was observedchanges of tone. In case of a RGB tri-color mixture type, because of alarge specific gravity of the red (R) fluorescent element, thisfluorescent element migrated vertically downward, and an increase of thex value of the chromaticity coordinates was observed.

FIG. 6 is a graph that shows measured changes of chromaticity x withcurrent-supply time. As shown there, in case a gel-like silicone resinis used as the material of the sealing element 111, the chromaticity xbegins to increase from near 100 hours of the current supply time, andexhibits an accelerative increase beyond 1000 hours. In contrast, incase a rubber-like silicone resin is used, no tone change was observedeven after operation of 10000 hours under raised temperatures of thelight emitting device due to the electric supply. It is presumed thatthe rubber-like silicone resin, hard and closely packed, was less likelyto permit diffusion of the fluorescent element.

(2) Since gel-like silicone resins are soft, although the stress theygive to the light emitting element 106 and the wires 108, 109 is small,they are weak against the external force. That is, the light emittingdevice as shown in FIG. 1 is used as a “surface-mounting type” lamp, forexample, and mounted on a packaging substrate with an assemblyapparatus. In this process, a vacuum collet of the assembly apparatus isoften pressed against the surface of the sealing element 111. In case agel-like silicone resin having a JISA hardness in the range of 30 to 40is used, the sealing element 111 may be deformed by the pressing forcefrom the vacuum collet, which in turn may deform the wires 108, 109 orgive a stress to the light emitting element.

In contrast, rubber-like silicone resins having a JISA hardness in therange of 50 to 90 are prevented from deformation by a selector or anassembler used for selecting or assembling light emitting devices.

As explained in Paragraphs (1) and (2) above, the

Inventors have confirmed that the use of a rubber-like silicone resininstead of a gel-like silicone resin can remarkably improve the emissioncharacteristics, reliability, mechanical strength, and so forth.

A technique for increasing the hardness of a silicone resin is to add anagent for giving a thixotropy index.

On the other hand, when a scattering agent is added together with thefluorescent element 110 to the silicone resin as the sealing element, itis possible to scatter and evenly deliver primary light from the lightemitting element 106 to the fluorescent particles and to scatter thelight from the fluorescent element 110 so as to realize a uniformmixture of colors. This contributes to realization of desired emissioncharacteristics even with a less quantity of fluorescent element 110.

(Placement of the Element in the Opening 105)

The light emitting device according to the embodiment of the inventionuses a semiconductor light emitting element made of a nitridesemiconductor having a short wavelength shorter than 400 nm. To ensure asufficient reliability with the light emitting element, it is necessaryto connect a protective Zener diode in parallel. Therefore, in the lightemitting device according to the embodiment of the invention, it isimportant to efficiently place the light emitting element 106 and theprotective Zener diode in a limited space inside the opening 105.

FIG. 7 is a diagram that schematically illustrates a planarconfiguration inside an opening of a light emitting device according tothe embodiment of the invention.

In the specific example shown in FIG. 7, an approximately ellipticalopening is formed in the resin stem 100. On the bottom 105 of theopening, distal ends of a pair of leads 101, 102 are formed. Opposed endportions of the leads 101, 102 have formed slits 101G, 102G. The lightemitting element 106 is mounted on an end portion 102B of the lead 102,and the Zener diode 150 is mounted on and end portion of the lead 101.That is, the light emitting element 106 and the Zener diode 150 aremounted at diagonal positions.

A wire 109B extending from the light emitting element 106 is connectedto the lead 101B, and a wire 109C is connected to the lead 102. A wire109A extending from the Zener diode 150 is connected to the lead 102A.The other electrode of the Zener diode is formed on the back surface ofthe diode and directly connected to the lead 101A.

In the layout pattern shown in FIG. 7, the approximately ellipticalshape of the opening increases the opening area, thereby increases thespace for accommodating two elements 106, 150, and makes it possible tolocate the light emitting element 106 as close as possible to the centerof the opening 105.

The elliptical opening also provides the space for bonding the wires. Toconnect the wires 109A through 109C to the leads 101, 102, the space forinserting the collet of the bonding apparatus is necessary. The layoutof FIG. 7 makes the space for inserting the bonding collet at each sideof the light emitting element 106 and the Zener diode 150 diagonallylocated. Furthermore, three wires are prevented from intersecting witheach other.

Moreover, the layout pattern shown in FIG. 7 permits three wires 109Athrough 109C to extend along the outer circumference of the ellipticalopening 105 to further alleviate the stress by the sealing element 111.

Heretofore, the first embodiment of the invention has been explainedwith reference to FIGS. 1 through 7.

There follows an explanation of modifications of the invention.

SECOND EMBODIMENT

Next explained is the second embodiment of the invention.

FIG. 8 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the second embodiment of the invention. Among componentsshown here, the same or equivalent components as those already explainedwith reference to FIGS. 1 through 7 are commonly labeled, and theirdetailed explanation is omitted for simplicity.

The light emitting device 1B shown here also includes a resin stem 100,semiconductor light emitting element 106 mounted thereon, and sealingelement 111 embedding the element 106.

In this embodiment, however, the sealing element 111 containing thefluorescent element 110 merely embeds the light emitting element 106,and a second sealing element 213 of a transparent resin is providedoutside the sealing element 111.

The limitative use of the sealing element 111 containing the fluorescentelement only to enclose the light emitting element 106 mounted at thebottom of the opening 105 contributes to increasing the luminance of thesecondary light. That is, because the size of the emission portion forreleasing the secondary light decreases, the luminance increases, andthe function of the reflective surface 104 to gather rays of light isenhanced.

Moreover, since the sealing element 111 containing the fluorescentelement is formed small at the bottom portion surrounded by the sidewall, external light is unlikely to intrude. Thereby, undesirableexcitation of the fluorescent element by external light can beprevented.

Furthermore, the embodiment shown here can realize a reliable lightemitting device free from breakage of wire by the resin stress becausethe sealing element 111 embeds the entirety of the Au wires 108, 109. Ifthe wires partly project into the second sealing element 213, they willreadily break due to a stress produced at the interface between thesealing elements 111, 213. In this embodiment, however, since the wires108, 109 are entirely embedded by the sealing element 111, they are freefrom breakage.

The second sealing element 213 is preferably made of an epoxy resin or asilicone resin to ensure close contact with the resin portion 103 andthe sealing element 111 and to improve the moisture resistance. Evenwhen an epoxy resin is used as the material of the second sealingelement, change of color or deterioration thereof can be preventedprovided substantially all of the primary light emitted from the lightemitting element 106 is converted to visible light by the sealingelement 111.

THIRD EMBODIMENT

Next explained is the third embodiment of the invention.

FIG. 9 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the third embodiment of the invention. Here again, the sameor equivalent components as those already explained with reference toFIGS. 1 through 8 are commonly labeled, and their detailed explanationis omitted for simplicity.

The light emitting device 1C shown here also includes a resin stem 100,semiconductor light emitting element 106 mounted thereon, and sealingelement 111 embedding the element 106.

Similarly to the second embodiment, the sealing element 111 containingthe fluorescent element 110 merely embeds the light emitting element106. In this embodiment, however, the space outside the sealing element111 remains open, without being filled by any other sealing element.

Here again, the limitative use of the sealing element 111 containing thefluorescent element only to enclose the light emitting element 106mounted at the bottom of the opening 105 contributes to increasing theluminance of the secondary light. That is, because the size of theemission portion for releasing the secondary light decreases, theluminance increases, and the function of the reflective surface 104 togather rays of light is enhanced.

Especially, in the instant embodiment, since the approximatelyhemispheric sealing element 111 serves as the emission point, and thereflective surface 104 surrounds it, the same optically convergingeffect as a conventional lamp can be obtained.

Furthermore, similarly to the second embodiment, external light isunlikely to intrude. Thereby, undesirable excitation of the fluorescentelement by external light can be prevented.

Furthermore, since the sealing element 111 embeds the entirety of the Auwires 108, 109, it prevents breakage of wire by a resin stress, andensures a high reliability.

FOURTH EMBODIMENT

Next explained is the fourth embodiment of the invention.

FIG. 10 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the fourth embodiment of the invention. Here again, thesame or equivalent components as those already explained with referenceto FIGS. 1 through 9 are commonly labeled, and their detailedexplanation is omitted for simplicity.

Similarly to the first embodiment, the light emitting device 1D shownhere also includes a resin stem 100, semiconductor light emittingelement 106 mounted thereon, and sealing element 111 embedding theelement 106.

The embodiment shown here includes a convex transparent element 413 isprovided on the sealing element 111 to ensure the function of gatheringrays of light. The transparent element 413 may be made of a resin, forexample. Especially, an epoxy resin or a silicone resin is advantageousfor decreasing the difference of the refractive index from the sealingelement 111 and to reduce the loss by reflection at the interface withthe sealing element 111.

The convex shape of the transparent element 413 is not limited to aspherical shape. Any appropriate shape can be selected depending on therequired converging ratio or luminous intensity profile.

FIFTH EMBODIMENT

Next explained is the fifth embodiment of the invention.

FIG. 11 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the fifth embodiment of the invention. Here again, the sameor equivalent components as those already explained with reference toFIGS. 1 through 10 are commonly labeled, and their detailed explanationis omitted for simplicity.

Similarly to the first embodiment, the light emitting device 1E shownhere also includes a resin stem 100, semiconductor light emittingelement 106 mounted thereon, and sealing element 111 embedding theelement 106.

In the instant embodiment, however, the resin portion 103 has no sidewall around the sealing element 111 such that the secondary light fromthe fluorescent element 110 both upwardly and laterally to realize awide luminous intensity profile. This is suitable for applicationsexpected to provide a wide field of view or a wide field of emission.

Shapes of the sealing element and the resin stem 100 are not limited tothose illustrated. For example, the sealing element may be hemisphericalas shown in FIG. 12, and the resin stem 100 may have a resin portion 103configured to bury the leads 101, 102 and surround the element with alow side wall.

SIXTH EMBODIMENT

Next explained is the sixth embodiment of the invention.

FIG. 13 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the sixth embodiment of the invention. Here again, the sameor equivalent components as those already explained with reference toFIGS. 1 through 12 are commonly labeled, and their detailed explanationis omitted for simplicity.

The light emitting device 1F shown here also includes a pair of leads101, 102. However, the first lead 101 has formed a cup portion 601 atthe distal end, and the light emitting element 106 is mounted at thebottom of the cup portion 601. Then the wires 108, 109 extending fromthe light emitting element 106 are connected to the leads 101, 102,respectively. The sealing element 111 containing the fluorescent element110 is formed to embed these components.

The inner side wall surface of the cup portion 601 serves as thereflective surface to reflect the primary light from the light emittingelement 106 upwardly. In receipt of the primary light, the fluorescentelement 110 releases secondary light of predetermined wavelengths.

The light emitting device shown here replaces conventional lamp-typesemiconductor devices, and is operative as a general-purpose lightemitting device having a relatively wide field of emission.

SEVENTH EMBODIMENT

Next explained is the seventh embodiment of the invention.

FIG. 14 is a cross-sectional view that schematically shows aconfiguration of the substantial part of a light emitting deviceaccording to the seventh embodiment of the invention. Here again, thesame or equivalent components as those already explained with referenceto FIGS. 1 through 13 are commonly labeled, and their detailedexplanation is omitted for simplicity.

The light emitting device 1G shown here has a structure similar to thelight emitting device 1F according to the sixth embodiment. The lightemitting device 1G also has a cup portion 601 at the distal end of thefirst lead 101, and the light emitting element 106 is mounted at thebottom thereof. Then the wires 108, 109 from the light emitting element106 are connected to the leads 101, 102, respectively. The sealingelement 111 containing the fluorescent element 110 is provided to embedthose components.

In the instant embodiment, however, the sealing element 111 issmall-sized, and a transparent element 713 is provided to enclose thesealing element 111.

The small-sized sealing element 111 containing the fluorescent element110 diminishes the emission portion and increases the luminance. The topsurface of the transparent element 713 functions as a lens to gatherrays of light, and makes it possible to extract converged light as well.

The transparent element 713 enclosing the sealing element 111 isolatesthe fluorescent element 110 from the outside atmosphere and improves itsdurability against moisture and corrosive atmosphere. The transparentelement may be made of a resin. Especially, an epoxy resin or siliconeresin is advantageous for close contact with the sealing element 111 toenhance the resistance to whether and the mechanical strength.

The embodiment shown here is not limited to the illustrated example. Forexample, as shown in FIG. 15, the sealing element 111 containing thefluorescent element 110 may be limited only on the cup portion 601 toreduce the size of the emission portion and thereby increase theluminance. In this case, the wire 109 will extend beyond the boundarybetween the sealing element 111 and the transparent element 713.However, if the sealing element 111 and the transparent element 713 aremade of similar materials, the stress at the boundary will be minimizedand will prevent breakage of wire.

Heretofore, various embodiments of the invention have been explainedwith reference to specific examples. The invention, however, is notlimited to those examples. Rather, the invention should be construed toinclude various changes and modifications an ordinary skilled person canmake regarding, for example, the materials of the fluorescent elements,structures and materials of the light emitting element, shapes of theleads and the sealing element 111, dimensional relations amongcomponents, and so on.

While the present invention has been disclosed in terms of theembodiment in order to facilitate better understanding thereof, itshould be appreciated that the invention can be embodied in various wayswithout departing from the principle of the invention. Therefore, theinvention should be understood to include all possible embodiments andmodification to the shown embodiments which can be embodied withoutdeparting from the principle of the invention as set forth in theappended claims.

1. A light emitting device comprising: a light emitting element whichemits primary light; a silicone resin forming at least a part of anoutside surface of the light emitting device wherein said outsidesurface is concave, the silicon resin having a hardness in the range of50 to 90 in JISA value; a fluorescent element provided around the lightemitting element, the fluorescent element absorbing the primary lightand releasing visible light; and a resin portion having an opening, thelight emitting element being disposed at a bottom of the opening and,the silicone resin being provided to fill the opening.
 2. A lightemitting device according to claim 1, wherein the fluorescent elementincludes a first fluorescent material which absorbs the primary lightand releases first visible light, and a second fluorescent materialwhich absorbs the primary light and releases second visible lightdifferent in wavelength from the first visible light.
 3. A lightemitting device according to claim 2, wherein the first visible lightand the second visible light are chromatically complementary.
 4. A lightemitting device according to claim 1, wherein the fluorescent elementincludes a first fluorescent material which absorbs the primary lightand releases red light, a second fluorescent material which absorbs theprimary light and releases green light, and a third fluorescent materialwhich absorbs the primary light and releases blue light, the fluorescentelement providing white light by mixture of the red light, green lightand blue light.
 5. A light emitting device according to claim 1 furthercomprising a wire connected to the light emitting element, the siliconeresin being provided to embed the wire.
 6. A light emitting deviceaccording to claim 1, wherein the fluorescent element is contained inthe silicone resin.
 7. A light emitting device according to claim 1,wherein the fluorescent element includes a first fluorescent materialhaving a first specific gravity and a first grain size, and a secondfluorescent material having a second specific gravity and a second grainsize, the second specific gravity is different from the first specificgravity, and the second grain size is different from the first grainsize.